# Copyright 2017 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""Provides utilities that may be especially useful to plugins."""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import bleach

# pylint: disable=g-bad-import-order
# Google-only: import markdown_freewisdom
import markdown
import six

from tensorboard.backend import experiment_id as _experiment_id


_ALLOWED_ATTRIBUTES = {
    "a": ["href", "title"],
    "img": ["src", "title", "alt"],
}

_ALLOWED_TAGS = [
    "ul",
    "ol",
    "li",
    "p",
    "pre",
    "code",
    "blockquote",
    "h1",
    "h2",
    "h3",
    "h4",
    "h5",
    "h6",
    "hr",
    "br",
    "strong",
    "em",
    "a",
    "img",
    "table",
    "thead",
    "tbody",
    "td",
    "tr",
    "th",
]

# Cache Markdown converter to avoid expensive initialization at each
# call to `markdown_to_safe_html`.
_markdown = markdown.Markdown(extensions=["markdown.extensions.tables"])


def markdown_to_safe_html(markdown_string):
    """Convert Markdown to HTML that's safe to splice into the DOM.

    Arguments:
      markdown_string: A Unicode string or UTF-8--encoded bytestring
        containing Markdown source. Markdown tables are supported.

    Returns:
      A string containing safe HTML.
    """
    warning = ""
    # Convert to utf-8 whenever we have a binary input.
    if isinstance(markdown_string, six.binary_type):
        markdown_string_decoded = markdown_string.decode("utf-8")
        # Remove null bytes and warn if there were any, since it probably means
        # we were given a bad encoding.
        markdown_string = markdown_string_decoded.replace(u"\x00", u"")
        num_null_bytes = len(markdown_string_decoded) - len(markdown_string)
        if num_null_bytes:
            warning = (
                "<!-- WARNING: discarded %d null bytes in markdown string "
                "after UTF-8 decoding -->\n"
            ) % num_null_bytes

    string_html = _markdown.convert(markdown_string)
    string_sanitized = bleach.clean(
        string_html, tags=_ALLOWED_TAGS, attributes=_ALLOWED_ATTRIBUTES
    )
    return warning + string_sanitized


def experiment_id(environ):
    """Determine the experiment ID associated with a WSGI request.

    Each request to TensorBoard has an associated experiment ID, which is
    always a string and may be empty. This experiment ID should be passed
    to data providers.

    Args:
      environ: A WSGI environment `dict`. For a Werkzeug request, this is
        `request.environ`.

    Returns:
      A experiment ID, as a possibly-empty `str`.
    """
    return environ.get(_experiment_id.WSGI_ENVIRON_KEY, "")
